This invention relates generally to carburetors and more particularly to a carburetor with a fuel shut-off system.
It is known to use a carburetor to provide a fuel-and-air mixture to an engine to support combustion in and operation of the engine. If a hot or warmed-up engine is turned off under high speed conditions, such as for example, 3,600 r.p.m. or higher, an engine governor moves a carburetor throttle valve to its wide-open position permitting air flow through the carburetor; and the engine coasts to a stop. As the engine slows down, air is pulled into the engine and the carburetor continues to deliver fuel to the engine. With the ignition system turned off, the unburned fuel-and-air pass without being ignited through the engine and into the hot exhaust system downstream of the engine. Under certain conditions, the fuel-and-air may then ignite within hot regions in the exhaust system resulting in a loud boom or xe2x80x9cafter-firexe2x80x9d. Beyond the unsettling noise of the after-fire, the expanding gases from the ignited fuel-and-air mixture in the exhaust system can create sufficient pressure to damage the engine and exhaust components.
U.S. Pat. No. 4,111,176 discloses a float feed carburetor having a fuel bowl or chamber vent passage, a vacuum bypass passage and a solenoid valve operable to close the bowl vent passage when the vehicle ignition system is turned off to shut down the engine. Undesirably, the vacuum bypass passage remains open to the bowl vent passage in all positions of the solenoid valve and throughout the operation of the carburetor and engine. With this construction, an enlarged diameter bowl vent passage is required to prevent undue interference with the fluid flow through the fuel-and-air mixing passage of the carburetor due to the interaction between the vacuum bypass passage and fuel bowl vent passage.
Some carburetors have a solenoid valve attached to the bottom of the fuel bowls of the carburetor and operable to close the inlet of the fuel nozzle when the engine is shut-off. This requires a liquid tight seal between the fuel bowl and the solenoid valve, a specialized arrangement of the fuel nozzle and seat area for the solenoid valve, and heat from the solenoid valve can be transferred to the fuel in the fuel bowl.
A fuel shut-off system for a carburetor substantially reduces or prevents the delivery of fuel to an engine after the engine is turned off. The fuel shut-off system preferably reduces or eliminates the pressure differential across a nozzle through which fuel is delivered from a fuel chamber through the carburetor and into the engine. In this manner, the flow of fuel through the nozzle is reduced and preferably eliminated to prevent the after-fire and associated problems within a residually hot exhaust system.
An actuator, preferably a three-way electric solenoid valve, is operable to control the opening and closing of one or more carburetor vent passages to control the pressure differential across the nozzle. Desirably, the carburetor is a float feed carburetor having a fuel chamber in communication through the nozzle with a fuel-and-air mixing passage formed in the carburetor. When the combustion engine is running, the fuel chamber is vented to the atmosphere through a fuel chamber passage, and when the engine is not running or initially shut-down, the fuel chamber is communicated with the fuel-and-air mixing passage through a vacuum bypass passage.
When the engine ignition system is on and the engine is operating, the solenoid-controlled valve is in a running position closing the vacuum bypass passage and preferably opening an atmosphere passage which only then communicates with the fuel chamber passage. When the ignition system is turned off, to shut-off the engine, the solenoid-controlled valve is moved to a non-running position so that the vacuum bypass passage communicates with the fuel chamber passage and preferably the atmosphere passage is closed. This results in substantially equal pressure at an outlet of the nozzle in the area of the fuel-and-air mixing passage and at an inlet of the nozzle in the area of the fuel chamber. With the pressure being substantially equal across the fuel nozzle, fuel flow through the nozzle stops. Desirably, because the solenoid-controlled valve closes the vacuum bypass passage during normal operation of the engine and carburetor, the fuel chamber passage can be made smaller in size than in prior systems which left the vacuum bypass passage open at all times.
Objects, features and advantages of this invention include providing a carburetor with a fuel shut-off which prevents fuel flow to the engine after the engine is shut down, prevents after-fire, reduces engine exhaust emissions, enables use of a solenoid valve of reduced size, does not require a liquid tight seal between the solenoid valve and carburetor, eliminates the need for specially formed fuel jets and nozzles, avoids problems associated with solenoid heat transferred to the fuel bowl of a float feed carburetor, enables use of a smaller fuel bowl vent passage, is of relatively simple design and economical manufactured and assembly, and in use has a long service life.